Battery pack and method for calculating electric energy of battery pack

Abstract

A battery pack (10) includes a plurality of battery cells (100) which are connected in series to each other, a voltage and current measurement unit (voltage and current measurement unit (200)), a temperature measurement unit (temperature measurement unit (300)), and a calculation unit (calculation unit (420)) provided in an arithmetic operation communication unit (400). The calculation unit (420) calculates a “first electric energy balance” of the battery cells (100) on the basis of voltages and currents, determines internal resistances of the battery cells (100) on the basis of the temperatures, and calculates a “second electric energy balance” of the internal resistances on the basis of currents and the internal resistances. Thereby, the calculation unit (420) calculates an “accumulated electric energy balance” (electric energy E(t)) accumulated in the battery cells (100) on the basis of the first electric energy balance of the battery cells (100) and the second electric energy balance of the internal resistances.

The invention claimed is: 
     
       1. A battery pack comprising:
 a plurality of battery units which are connected in series to each other; 
 a voltage and current measurement unit that measures voltages and currents of the battery units; 
 a temperature measurement unit that measures temperatures of the battery units; 
 a calculation unit that calculates a power variation which is a variation of electric energy remaining in the battery units on the basis of the voltages, the currents and the temperatures of the battery units; and 
 a storage unit that stores internal resistance data which is data for calculating internal resistances of the battery units from the temperatures of the battery units, 
 wherein the calculation unit refers to the internal resistance data to determine the internal resistances of the battery units at a present temperature, and calculates, when the power variation of all the battery units from reference time 0 to current time t is set to ΔE(t), and a total internal resistance which is a total sum of the internal resistances of the battery units is set to R temp (t), the power variation ΔE(t) from the following Expression (1):
   [Expression 1] 
   Δ E ( t )=∫ 0   t   {V ( t ) I ( t )− I   2 ( t ) R   temp ( t )} dt   (1)
 
 
 (here, V(t) is a total voltage of all the battery units, and I(t) is a current of the battery units). 
 
     
     
       2. The battery pack according to  claim 1 , wherein in a state where a time of initial full charge is set to the reference time 0, the storage unit stores initial electric energy which is an electric energy at the reference time, and
 the calculation unit calculates a present electric energy by a sum of the initial electric energy and the power variation ΔE (t). 
 
     
     
       3. The battery pack according to  claim 2 , wherein the calculation unit calculates a deterioration ratio obtained by comparing an electric energy at a time immediately preceding full charge with the initial electric energy, and corrects the total internal resistance on the basis of the deterioration ratio. 
     
     
       4. The battery pack according to  claim 1 , further comprising a communication unit that transmits a signal based on the power variation ΔE (t) to an external device.